read masked and overviews when no-data value is defined

Guy Doulberg
 

Hi all,

We are trying to read masked array using `DatasetReaderBase.read`, reading the documentation it looks that if we pass masked=True we will get what we wanted. 

I was testing the read on raster with pre-built overviews and I used the overviews in read. From functionality point of view, I always got the right result, but I was tesing the data block that are being used, and I noticed this behaviors:


1. When using band-mask, there was a read only from the overview to construct the mask -- as excpected
2. When using no-data value there were reads the data of the original resolution and not from the nearest overview? when mask=False it reads data only from the overview,  why is that?

A workaround for that is to read with no mask and to construct the mask myself using the no-data value.

Thanks.

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